The functioning of a decoder is managed by a security module or chip card containing the data pertaining to a subscriber. This data comprise rights paid by the subscriber allowing him to decrypt audio and/or digital video programs broadcasted by an operator via a cable, a satellite or any other diffusion network.
Each operator has and manages a database containing the data related to the contract that each subscriber has agreed with the operator. These databases are connected to an access control system that one of its functions is the generation of management messages called EMM “Entitlement Management Messages”, that is to say messages containing the commands intended for a decoder or a group of decoders. These messages are broadcasted in the data stream of audio and/or video programs and are processed by the security module of the decoder. The latter stores the rights authorizing or not the decryption of a program that a subscriber has requested from an operator.
The document EP0989743 describes a method for transmitting, in a digital data stream, a table containing information concerning applications related to a set of services. This table allows namely to decide on the maintenance or not of certain applications during switching from one service to another included in a bouquet. The decoder stores the table in a memory and controls the downloading and the updating of the applications in function of the information contained in the table.
The document U.S. Pat. No. 5,742,677 discloses a subscriber terminal comprising a secured non-volatile memory configurable under the control of a local server or head end. The memory can be directly accessible by service providers, which transmit messages including commands without the intervention of the head end in condition that these providers are certified.
According to a known configuration, each digital television operator manages a group of subscribers having at least one functioning decoder with a security module provided by the operator. When a subscriber wishes to decrypt the programs of another operator, he is invited to replace the security module of the first operator with that of the second operator from whom he has bought the rights corresponding to programs that are only managed by this other operator. This change of security module is only possible with a decoder provided with a module in the form of a removable smart card or selectable cards inserted into several card readers.
This type of configuration presents a drawback at time of the increase of the number of specialized operators who each propose a card to be inserted into the decoder to be able to decrypt their programs. Therefore, a subscriber may be forced to change cards each time the type of program is changed. For example, during the showing of a sports program, then a film, then a variety program and then a sports program again, the subscriber may change the card up to three times.